This invention relates to methods and apparatus for disposing of radioactive wastes, and more particularly to methods and apparatus for solidifying radioactive waste liquids into hardened masses suitable for disposal by burying.
In particular this invention is an improvement upon the methods and apparatus shown and described in co-pending United States patent application Ser. No. 418,929, of Kenneth A. Gablin and Larry J. Hansen, filed Nov. 26, 1973.
As pointed out in said Gablin and Hansen application, radioactive wastes such as liquid waste materials from nuclear reactors are conventionally disposed of by burying them in the earth or dumping them at sea. To prevent contamination of the surrounding environment these waste materials, sometimes liquids containing solid radioactive waste materials in suspension, are incorporated in solid shielding bodies.
Various attempts have been made to obtain solid suspensions of these materials in a commercially acceptable manner. However, a number of problems are encountered, and none of the prior art expedients are completely satisfactory. Prior to the invention of Said Gablin and Hansen application solid radioactive wastes were fixed by means of glass, bitumen, asphalt and similar materials, and also by means of emulsified asphalt, polyester and polyethylene. The latter materials did not prove to be practicable, and almost all of the encapsulation of liquid radioactive waste materials prior to the advent of the invention of the said Gablin and Hansen application was accomplished by mixing them with Portland Cement and allowing the resulting concrete-like mass to harden.
As pointed out in said Gablin and Hansen application, however, many unsolved problems arose in connection with the use of Portland Cement and these problems were solved to a practical extent only upon the advent of the invention of that application, which provides a setting agent capable of solidifying large quantities of water (the liquid most often encountered in radioactive waste disposal problems) and holding this water and other radioactive waste materials in a solid body well suited for transportation and burial.
The described setting agent of said Gablin and Hansen application is a water extendable polymer consisting of an aqueous suspension of urea formaldehyde, usually in partially polymerized form. This material is very "forgiving" in critical areas of surface tension and pH and can be used in many proportions to form solids of various strengths. This setting agent is capable of taking up comparatively large volumes of water as the mass solidifies. Control over the rate of solidification is easily obtained by varying the amount of curing agent used, and the curing agent is a low-cost commercially available reducing agent. Increasing the concentration of the curing agent shortens the solidification time as well as the time necessary to obtain the full potential strength of the mass. Raising the temperature of the mass also speeds up the solidification action. The said Gablin and Hansen application discloses a system of apparatus for mixing, proportioning, holding, heating, etc., of radioactive waste material, the said setting agent, and the said curing agent in order to encapsulate radioactive waste materials from reactors and the like in solid bodies suitable for transportation and storage by burial.
The proportioning aspects of the methods and apparatus of said Gablin and Hansen application make it possible to provide a resulting solidified mass which meets the LSA (Low Specific Activity) standards imposed by law in connection with the transportation and handling of radioactive materials.
With the levels of radioactivity encountered in nuclear reactor waste materials it is usually necessary to provide shielding during the handling attendant upon encapsulation for transportation and burial. This shielding and the necessity for generally protecting the operator of the mixing apparatus from exposure to radiation to the maximum possible degree renders extremely difficult certain simple method steps which in processing nonradioactive substances would offer no substantial difficulty.
Thus, determining when a mass of admixed radioactive waste material and setting agent is fully solidified must be determined by indirect instrumental means, since the operator of the apparatus of the Gablin and Hansen invention cannot be directly exposed for extended periods to the mass of radioactive material and setting agent.
Further, it is highly desirable to prevent the occlusion of radioactive waste water on the top surface of the mixed, solidified mass of radioactive waste material and setting agent.
It is therefore a principal object of the present invention to provide methods and apparatus whereby the operator of apparatus of the kind shown and described in the said Gablin and Hansen application can without exposure to the admixed mass of radioactive waste material and setting agent accurately determine when the admixed mass is fully solidified.
It is a further object of the present invention that such method be capable of being carried out without the employment of expensive sensing means, which must be buried or otherwise disposed of with the solidified mass.
It is a yet further object of the present invention to provide a method whereby an operator of the apparatus shown and described in said Gablin and Hansen application can determine with accuracy the time when the mass of radioactive waste material and setting agent is fully solidified but occlusion of waste water has not gone forward to a substantial degree.
It is an additional object of the present invention to provide methods whereby operators of apparatus of the kind shown and described in said Gablin and Hansen application can, after flowing coating material such as substantially pure urea formaldehyde over the mass, determine when this coating material has substantially completely absorbed the occluded surface water.
Other objects and features of the advantage inherent in the methods and apparatus of the present invention will become apparent as the specification and claims continue.